Taxol (paclitaxel), a complex diterpene, is currently considered the most exciting lead in cancer chemotherapy. Paclitaxel possesses high cytotoxicity and strong antitumor activity against different cancers which have not been effectively treated by existing antitumor drugs. For example, paclitaxel has been approved by FDA in late 1992 for the treatment of advanced ovarian cancer and for breast cancer in 1994. Paclitaxel is currently in phase II and III clinical trial for lung cancer and other cancers.
Although paclitaxel is an extremely important "lead" in cancer chemotherapy, it is common that better drugs can be derived from naturally occurring lead compounds. In fact, French researchers have discovered that a modification of the C-13 side chain of paclitaxel brought about a new anticancer agent which seems to have antitumor activity superior to paclitaxel with better bioavailability. This unnatural compound was named "Taxotere (docetaxel)", which has t-butoxycarbonyl instead of benzoyl on the amino group of (2R,3S)-phenylisoserine moiety at the C-13 position and a hydroxyl group instead of acetoxy group at C-10. Docetaxel is currently in phase II and III clinical trials in United States, Europe, and Japan, has shown excellent activity, especially against breast and lung cancers. ##STR2##
A recent report on clinical trials of paclitaxel and docetaxel has disclosed that paclitaxel causes, e.g., nerve damage, muscle pain or disturbances in heart rhythm, whereas docetaxel provokes, e.g., mouth sores and a plunge in white blood cells. Other less serious side effects also exist for these two drugs. Therefore, it is very important to develop new anti-cancer drugs different from these two drugs which have fewer undesirable side effects, better pharmacological properties, improved activity against drug-resistant tumors, and/or activity spectra against various tumor types.
It is an objective of the present invention to develop such new anti-tumor agents of paclitaxel class, i.e., taxoids, which have distinct structural differences from those of paclitaxel and docetaxel.
It is an object of the present invention to provide a series of new taxoids bearing a 1-propenyl, 2-methyl-1-propenyl, 2-methylpropyl, or trifluromethyl radical at the C-3' position instead of a phenyl group, and which possess strong antitumor activities with better therapeutic profile, in particular against drug-resistant tumors. One of the serious drawbacks of both paclitaxel and docetaxel is the fact that these two drugs possess only a weak activity against drug-resistant tumors, e.g., adriamycin-resistant breast cancer. The new taxoids of the present invention have shown not only stronger antitumor activities against human ovarian, non-small cell lung, colon, and breast cancers than those of the two drugs, but also exhibit more than one order of magnitude better activity against adriamycin-resistant human breast cancer cells than those of the two drugs. Multi-drug-resistance (MDR) is a serious issue in clinical oncology, and thus the new taxoid antitumor agents of this invention will serve as important drugs to overcome this problem.